The present invention relates to combined cycle electric power generating plants and, more particularly, to inlet guide vane modulations of the vanes of the gas turbines included therein. Further, the present invention relates to inlet guide vane control apparatus adapted to modulate the gas turbine guide vanes either automatically or manually having further provision for bumpless transfer therebetween.
In the operation of combined cycle and other electric generating power plants which employ at least one gas turbine, it is desirable to achieve maximized operating efficiencies or high heat rates. Ordinarily, gas turbines are operated at base load because of poor heat rates at reduced load. However, in the combined cycle plant or in the case of larger gas turbines, reduced load operation of the gas turbine is often a necessity since the full generating capability of the plant or turbine is not always required. Consequently, modulating the inlet guide vanes of the gas turbine at reduced loads is undertaken in order to improve heat rate and increase the gas turbine exhaust temperature, which increase is then utilized to supplement the afterburner and steam generator functions.
The modulation of the inlet guide vanes of a gas turbine for differing purposes is known. For example, in the aforementioned application Ser. No. 323,593, the inlet guide vanes are positionally controlled to hold gas turbine exhaust temperature at a constant value over its operating range in order to simultaneously generate power and drive an external, unrelated process. In particular, such operation is achieved as a function of a temperature control loop and the combustor shell pressure. In U.S. Pat. No. 3,623,326 issued to C. Greune on November 30, 1971, inlet guide vane modulation is utilized to maintain a constant, high exhaust gas temperature, both during acceleration and in steady-state performance of a gas turbine driven vehicle. In particular, such control is effected as a function of throttle position. Reference may also be had to commonly assigned and copending application Serial No. 319,114 and the related cases cited therein for a further example of inlet guide vane regulation as a function of speed.
None of these prior art arrangements are particularly suitable for use in a combined cycle generating plant. Neither are any of the known alternative schemes as is perhaps best exemplified by U.S. Pat. No. 3,097,486 issued to R. Roe on July 16, 1963. In the Roe patent, the entire exhaust of the gas turbine is delivered to a steam furnace for utilization therein as a function of speed or air flow control means which sense the plant power demands. Thus, as load demand on the system varies and the compressor output is regulated by the speed or air flow control means, the rate of flow through the furnace is regulated such that the higher the loading, the higher the exhaust temperature of the turbine and, conversely, the lower the loading, the cooler the exhaust temperature.
In order to improve heat rates and increase the overall plant efficiency, it is necessary at lower gas turbine loading to utilize exhaust temperature as a supplemental heating source for steam generation. While the Roe patent comes closest to this, it and the other known prior art arrangements do not satisfactorily achieve the desired result.
It should be noted that the description and understanding of the prior art discussed hereinabove is made in good faith and on the representation that the prior art referred to or considered may not be the most pertinent or that the conclusions desired are unrebuttable.